The disclosed subject matter relates generally to separating fluids in a process stream and, more particularly, to an electrostatic coalescer for coalescing fluids that are primarily gas.
The separation of water from a hydrocarbon liquid is an important process in the oil production industry. In an oil dominated regime, small water droplets can occur in the continuous oil phase due to shearing in upstream piping, for example. The droplet size is an important contributing factor to the speed of the separation. Small droplets of water in oil separate slowly from the oil compared to larger droplets due to the immiscibility of the liquids and the differences in specific mass.
One conventional approach for oil/water separation makes use of gravity and requires large residence times inside separators. Large residence times are needed for an acceptable separation performance, and therefore this approach is not suitable for an in-line application with high flow rates. Other techniques that use chemicals to break the emulsions require later removal of the chemicals, thereby increasing cost. Still other techniques that employ heating are less effective at breaking emulsions.
The separation of liquids from fluid streams that are primarily gas is also an important process in industry. In many cases, gases with a high economical value are obtained containing very fine droplets of liquids. Examples may be natural gas or many other gases used in the chemical industry, such as chlorine or sulfur dioxide. Also, in process industry, vapors may partly condense, which may also result in gas containing fine liquid droplets, especially in high gas speed applications (i.e., the high speeds provide significant force to draw the droplets along). Further, any obstacle in the flow path may generate high and low pressure areas, resulting in more condensation at the obstacle than compared to low gas speed application, where the pressure differences are much lower.
As these droplets can corrode piping and are harmful for pumps and other processing equipment, they should be removed before packing or transporting the commercial gas or using the gas in a process industry. Further, consumers want their products as pure as possible, and extraneous liquids lower the quality of these gases. In the petrochemical industry, especially off shore, where natural gas is obtained together with salt water and oil, it is beneficial to remove the water and/or other liquids as near to the well as possible. A significant effort is spent drying the natural gas to remove water vapor to concentrations far below saturation with water absorbers. However, such efforts may be inefficient if the gas to be dried contains liquid water in addition to vapors.
Conventional techniques for removing liquids from gases typically aim at improving the traditional separation of liquids from gases by using gravitation-like forces. One very old technique is based on the observation that a piece of cloth hanging in a fog will collect water from the fog, thus decreasing the fog intensity and providing water. The cloth acts as a condensation center for the droplets and gravitation will, in the case of water, cause excess water to flow down. This technique is the basis for the separation of liquids from gases using a mesh wire.
Another technology involves increasing the gravitational forces to make the suspension of liquid droplets more instable in the gas. Gravitational forces can be increased by spinning the medium, which results in a centripetal force of many times normal gravitation. In this manner, the separation proceeds at a rate many times faster than under gravitation alone, resulting in a much smaller apparatus.
Still, for large scale in-line operation both mesh wire technologies and accelerators have their disadvantages. A mesh can become clogged and requires the gas molecules to follow complicated paths through the mesh, costing mechanical energy. Increasing gravitational forces by spinning also requires mechanical energy that is generally drawn from the gas to be separated. This consumed mechanical energy results in a pressure drop, which increases the required number or size of the pumps. Further, both techniques require sensitive equipment that is vulnerable to erosion.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.